The present invention relates to a low-pressure, hollow cathode lamp being filled with nitrogen and oxygen, and in which NO molecules emit radiation upon being energized by a low, electric current.
The German printed patent application No. 2,240,365 discloses such a lamp, particularly for use as a radiation source in a photometric gas analyzer, which is to measure the NO concentration in a mixture of gases. This particular hollow cathode lamp is filled with air at a pressure of from 1 millibar to 5 millibars. The discharge current is kept quite low (at about 1 milliampere, or less) so that the temperature of the air filling in the lamp is and remains almost the same as the ambient temperature.
It is inherent in lamps and radiation sources of the type referred to above that sputtering and clean-up consumes the gases in the body of the lamp; particularly, the oxygen is consumed in time so that, gradually, the intensity of the NO spectrum is reduced. After all of the oxygen has been consumed, the lamp will no longer be able to emit NO molecular resonance radiation.
It is obvious that the extension of the life of such a lamp is an important task. Even more so if such a lamp is the "weak link" in the analyzer of which it forms a part.